Copper activated thermoluminescence dosimeter and method

ABSTRACT

A novel copper activated thermoluminescence dosimeter comprising a glass composition having: about 94-97 weight percent SiO 2  ; about 0.4 to 2 weight percent Al 2  O 3  ; about 0.02 to 1 weight percent M 2  O, where M comprises Na +   or K +  ; about 2 to 6 weight percent B 2  O 3  ; and Cu(I), where Cu(I) is present at a level between about 10 18  to 10 19  ions/cm 3  ; method of making the same.

This is a divisional of copending application Ser. No. 08/393,936, filedFeb. 22, 1995.

This invention relates to a thermoluminescence dosimeter (TLD) glasscomposition which is useful for X ray or radiation and process for thepreparation of such a composition.

Crystals and glasses on exposure to high energy radiation like X-rays,γrays and to particle radiations, like and particles, frequently sufferstructural damage. Such irradiated crystals or glasses on subsequentthermal annealing get back to their original structure some time withthe emission of luminescence which is commonly known asthermoluminescence (TLD). Thermoluminescence phenomenon of such amaterial being an outcome of high energy irradiation, it cansuccessfully be used in estimating the radiation dose experienced by thematerials. The phenomenon of using thermoluminescence property of amaterial in determining the radiation level of a high energy radiationenvironment is known as thermoluminescence dosimetry (TLD) and thedevice made on this principle is known as thermoluminescence dosimeter.

A thermoluminescence dosimeter is commonly used in personal monitoring(i.e. to monitor the radiation dose experienced by a person working insuch a radiation environment) and in medical applications, e.g.radiation therapy. In each case, a thermoluminescence dosimeter is usedin the form of a badge. In the recent years, however, attempt has beenmade to use such dosimeter in monitoring high level radiation sourcesfrequently used in industries related to chemical technology (such aspolymerization, vulcanization of rubber, cracking of hydrocarbon), foodprocessing and materials testing.

A thermoluminescence dosimeter, used for the above describedapplications is superior to other dosimeter systems because of thefollowing qualities:

1. It gives stable response in widely varying environmental conditions.

2. It is reusable.

3. Incurs low average cost per dose measurement.

A variety of thermoluminescence phosphors like Calcium Sulphate:Dysprosium (CaSO₄ :DY), Lithium Fluoride TLD-100 (LiF, TLD-100), CalciumSulphate:Thulium (CaSO₄ :Tm), Lithium Fluoride TLD-600 (LiF TLD-600) areknown which are regularly used in X-ray and -ray dosimetry. However, inmost of the cases, they are used in low-level radiation detectionbecause of their low-level saturation limit (˜10⁴ R). On the other hand,radiation doses used in Chemical technology or in food processing,materials testing lie in the range 10⁴ -10⁸ R. Hence, conventionalthermoluminescence materials are not suitable for such high leveldosimetry.

The present invention provides a process for the preparation of a novelcopper activated thermoluminescence dosimeter (T.L.D.) glass havingrelatively wider measurable range which can be successfully used in lowlevel and to some extent in high level (˜10⁶ R) X-ray and -raydosimetry.

The glass composition of the present invention is novel and bears anultimate composition (wt %) SiO₂ =94-97%, Al₂ O₃ =0.4-2%,M₂ O=0.02%-1%(M=Na^(+/K) ⁺),B₂ O₃ =2-6% and Cu(I)=10¹⁸ -10¹⁹ ions/cm³. Upon X or-irradiation and subsequent thermal stimulation the glass emitsthermoluminescence (TL). We name the glass developed in the presentinvention as Alumino-silicate: Copper TLD glass (Al--Si:Cu TLD glass)which structurally consists of a network of tetrahedral silica withfrequent aluminum (+3) substitution in the sites of silicon. The cuprousions (Cu⁺¹) in the glass preferentially reside at the aluminum sites ascompensating cations. Upon X or -irradiation of the glass `hole` centresof the type [AlO₄ /Cu] are generated which act as thermoluminescencecentre on subsequent thermal stimulation.

The main advantages of the invention are as follows:

1. It is a glassy T.L.D. material having greater chemical stabilitytowards humidity and normal temperature conditions.

2. The material has superior reusability compared to other conventionalT.L.D. materials.

3. Larger measurable dose range.

Accordingly, the present invention relates to a process for thepreparation of a novel thermoluminescence dosimeter (T.L.D.) glass whichcomprises:

a) Preparation of a silicate glass of composition (mol %) SiO₂ =62-67%,B₂ O₃ =24-28%, M₂ O=6-8% (M=Na⁺ or K⁺) Al₂ O₃ =1-3%, CO=0.5-1% bymelting at a temperature in the range of 1400°-1500° c.

b) Casting of the glass in the shape of a slab.

c) Cutting of the glass in the form of plates of dimensions (40-50mm)×(15-30 mm)×(3-5 mm).

d) Heat-treating the glass plates at 550°-600° for 20-30 hours toachieve a phase separation of soluble borate phase out of the insolublesilica phase.

e) Leaching out of the soluble borate phase from the glass firsttreating with hot (90°-100° C.) distilled water for 10-24 hours thenwith dilute 0.1-0.3/N hydrochloric acid for 40-60 hours.

f) Finally repeatedly washing the leached porous glass with distilledwater until all chloride ions are removed from the glass.

g) The silica rich porous glass thus obtained had the composition (wt.%) SiO₂ =94-97%, Al₂ O₃ =0.4-2%, M₂ O=0.02-1.0% (M=Na⁺ /K⁺) and B₂ O₃=2-6%. Using this porous glass plates we have prepared the Cu(I)activated thermoluminescence dosimeter (TLD) glass as follows.

h) Firing of the porous glass in a furnace at a temperature in the rangeof 500°-700° C. under constant flow of air to burn out trappedimpurities in the pores of the glass.

i) Cooling the porous glass to room temperature.

j) Impregnating the glass with a solution of an organo-copper complex inan organic solvent.

k) Drying the impregnated glass in the temperature range 30°-50° C.

l) Slowly heating the composition initially in air up to 400°-600° C.for 3-4 hours then under a constant flow of an inert gas or inert +hydrogen gas up to 900°-1000° C. for 6-10 hrs.

m) Sintering the glass into monolithic plate at a temperature in therange of 1100°-1200° C.

The porous composition prepared may be preferably made in the form ofplates and the organo-copper complex used may be selected out offollowing compounds: copper-biurate, tetraammino copper,cupro-dipyridine, cuprous chloride.

The organic solvent used in preparing the solution of the copper complexis selected out of the following solvents: Ethanol, acetone, benzene,diethyl ether, pyridine and the like. The concentration of the complexused may range 1-3% (wt.).

The inert gas used is selected out of the gases like Argon, Helium andNitrogen.

A glass obtained by the process described above of the present inventionis perfectly colourless and contains almost all copper in the monovalentstate.

The invention as illustrated by the examples given below should not beconstrued to limit the scope of the invention.

EXAMPLE - 1

A porous glass of compositions (wt. %), SiO₂ =96%, B₂ O₃ =3%, Al₂ O₃=1%, Na₂ O=0.06% in the shape of a plate of dimensions (20 mm×50 mm×5mm) was prepared by following the methods described in thespecification. It was fired slowly up to a temperature of 600° C. underconstant flow of air to burn out all the organic matters trapped in thepores--it was then cooled to room temperature (30° C.) impregnated witha 2 percent (wt.) solution of cuprodipyridine in pyridine--thecomposition was allowed to dry at ambient temperature then heated veryslowly up to a temperature of 500° C. in air for 4 hours and then inArgon atmosphere up to a temperature of 1000° for 10 hours and finallyit was sintered into a monolithic glass at 1150°-1200° C. in Argonatmosphere. The product was a successful thermoluminescence dosimeter(TLD) glass having composition (wt. %), SiO₂ =96%, B₂ O₃ =3%, Al₂ O₃=1%, Na₂ O=0.06%, Cu(I)=2.5×10¹⁸ ions/cm³.

EXAMPLE - 2

In another experiment we prepared a porous glass of composition (wt. %)SiO₂ =95%, B₂ O₃ =2.5%, Al₂ O₃ =2%, Na₂ O=1% in the form of plate ofdimensions (20 mm×40 mm×3 mm). The glass was slowly heated in air up to50° for 3-4 hours to burn out the trapped impurities--cooled to 40°-50°C. then impregnated with a 0.5% (wt.) cuprous chloride solution inacetone--the composition was dried at ambient temperature--heated slowlyin argon atmosphere up to 900° C. for 6 hours and finally sintered intoa monolithic mass at 1100°-1150° c. in a reducing atmosphere of 10% (V)hydrogen+90% (V) argon. The glass obtained in this case was also asuccessful thermoluminescence dosimeter (TLD) glass of composition (wt.%) SiO₂ =95%, B₂ O₃ =2.54, Al₂ O₃ =24, Na₂ O=1% and Cu(I) 1×10¹⁹ions/cm³.

EXAMPLE - 3

In a third method we prepared a porous glass of composition (wt. %) SiO₂=94%, B₂ O₃ =34, Al₂ O₃ =24, Na₂ O=0.05% in the shape of a plate ofdimension (15 mm×40 mm×3 mm). It was very slowly fired in air at 500° C.for 5 hours to burn out the trapped impurities--cooled to 40°-50° C.then impregnated with a 1% (wt.) ethanolic solution of copper-biurate.The composition was dried at ambient temperature--then slowly heated inair up to 500°-600° C. for 3-4 hours. The temperature was slowly raisedup to 1000° C. Under a constant flow of helium gas in a duration of 6hours and finally it was sintered into a monolithic glass at 1100°-1150°C. under a reducing atmosphere of 10% (V) hydrogen and 90% (V) ofhelium. The product was a good thermoluminescence dosimeter glass ofcomposition (wt. %) SiO₂ =94%, B₂ O₃ =3%, Al₂ O₃ =2%, Na₂ O=0.05% andCu(I) ˜3.6×10¹⁸ ions/cm³.

The glass prepared is used in the powdered form for thermoluminescencedosimetric application. A calibration curve of thermoluminescence (T.L.)efficiency of the glass against the intensity of irradiation dose shouldfirst be made. For this purpose 4-5 samples of the powdered glass ofdefinite weight (5-10 mgs) dispersed on some suitable substrate (e.g.Teflon) are exposed either to X-ray or γ- radiation (source ⁶⁰ Co) ofknown radiation flux. However, exposure time of the sample should differfrom one another to make their radiation dose different.Thermoluminescence glow flux of each of the irradiated glass sample ismeasured quantitatively in a thermoluminescence set-up by heating thesample in the temperature range 50°-350° C. in an argon atmosphere.

The thermoluminescence glow flux of each of the sample is then plottedagainst respective radiation dose.

An unknown X or -ray dose level can be monitored just by exposing aknown quantity of the same powdered glass in the X or -ray environmentone desire to monitor, for a certain period of time and comparing itsthermoluminescence glow flux with respect to the respective curve.

The glass, however, does not show thermoluminescence property if thecopper ions in it do not remain in monovalent state. The copper ionconcentration in the glass may be in the range 10¹⁸ -10¹⁹ ions/cm³. Theglass attains radiation saturation in the dose level greater than 10⁶Rad.

What is claimed is:
 1. A process for preparing a copper activatedthermoluminescence dosimeter, the process comprising the steps of:(a)providing a silicate glass composition comprising: in moles, about 62-67percent SiO₂ ; in moles, about 24-28 percent B₂ O₃ ; in moles, about 6-8percent M₂ O, where M is Na⁺ or K⁺ ; in moles about 1-3 percent Al₂ O₃ ;in moles, about 0.5-1 percent CO; wherein said silicate glass has amelting temperature of about 1400°-1600° C.; (b) treating the silicateglass composition at a temperature and for a time sufficient to achievephase separation of a soluble borate phase out of an insoluble silicatephase; (c) leaching the soluble borate phase from the insoluble silicaphase by first treating the composition with distilled water wherein thedistilled water is at a temperature sufficient to achieve leaching ofthe soluble borate phase, and then treating the composition with about0.1N to 0.3N hydrochloric acid for a time sufficient to yield a leached,porous glass; (d) washing the leached glass to remove chloride ions toyield a silica rich porous glass having approximately: by weight 94 to97 percent SiO₂ ; by weight, 0.4 to 2 percent Al₂ O₃ ; by weight, 0.02to 1.0 percent M₂ O, where M is Na⁺ or K⁺ ; and, by weight, 2 to 6percent B₂ O₃ ; (e) heating the silica-rich porous glass at atemperature sufficient to remove impurities from the pores of the glass;(f) impregnating the silica-rich glass with a solution of anorgano-copper complex in an organic solvent; (g) drying, and thenheating, the impregnated glass in air to a sufficient temperature andfor a sufficient time to remove the organic solvent; and (h) treatingthe impregnated glass with a constant flow of (i) inert gas or (ii)inert gas and hydrogen gas.
 2. The process of claim 1 wherein theorgano-copper complex comprises copper biureate, tetraamino-copper,cupro-dipyridine, or cuprous chloride.
 3. The process of claim 2 whereinthe concentration of organo-copper complex in the composition is, byweight, 1-3 percent.
 4. The process of claim 1 wherein the inert gascomprises Nitrogen, Argon, or Helium.
 5. In a dosimeter comprising aglass powder dispersed in a substrate, the improvement comprises saidglass powder having an ultimate composition including:(a) about 94-97percent by weight SiO₂ ; (b) about 0.4 to 2 percent by weight Al₂ O₃ ;(c) about 0.02 to 1 percent by weight M₂ O, where M is Na⁺ or K⁺ ; (d)about 2 to 6 percent by weight B₂ O₃ ; and (e) Cu(I), wherein Cu(I) ispresent between about 10¹⁸ to 10¹⁹ ions/cm³.